Field of the Invention
The invention relates to a coupling for coaxial cables. Each of the two coaxial cables to be coupled to one another has a central conductor, which is surrounded by an outer conductor. Each coaxial cable has a coupling piece associated therewith, each of which has a connecting area which is electrically connected to the central conductor of the coaxial cable associated with it. A connection head, which is provided in order to produce an electrical contact with the connecting area of the first coupling piece and is mounted on it such that it can move, of the second coupling piece is supported on its connecting area via a spring element.
A coupling such as this is disclosed, for example, in European published patent application EP 0 314 299 A1. Couplings for coaxial cables with spring-mounted connection elements are also disclosed in the prior U.S. Pat. Nos. 3,416,125, 4,012,105, and 6,053,777.
A coupling such as this may be important in many industrial applications wherein coaxial cables must be disconnected from one another and reconnected quickly and easily, for example for maintenance work. In particular, a coupling such as this may be used with rigid coaxial conductors, such as those used for the transmission of electrical signals or pulses in a nuclear installation or in a nuclear power station installation.
In nuclear power station installations, the filling level of an operating or cooling medium in a container which cannot be looked into directly must be monitored and, if required, readjusted, for example the filling level of the primary coolant in the reactor pressure vessel. The so-called TDR (time domain reflectometry) measurement principle may be used for this purpose, as is known, by way of example from German patent DE 199 58 584 C1 (corresponding to U.S. Patent Application Publication No. 2002/0186025). The TDR measurement principle makes use of the effect that an electromagnetic pulse which is carried in an antenna system is partially reflected when the impedance between, for example, a central conductor of the antenna and an outer conductor which surrounds it in the form of a coaxial cable changes abruptly.
An abrupt change in the impedance such as this occurs, for example, where the antenna that is formed in this way enters a liquid from a gaseous environment, since the impedance depends on the capacitance between the central conductor and the outer conductor, and thus on the dielectric constants of the medium filling the space between the central conductor and the outer conductor. An electromagnetic pulse which is passed to an antenna such as this that is immersed in the medium to be monitored is thus partially reflected on the surface of the medium. A further reflection occurs at the normally short-circuited antenna end. Since, apart from this, the propagation speed of the electromagnetic pulse in the antenna is known, the propagation time difference between the pulse reflected on the boundary layer and the pulse reflected at the antenna end can be used as a measure of the position of the boundary layer, and thus as a means for determination of a position value which is characteristic of the position of the boundary layer, wherein case it can be assumed that there is an essentially proportional relationship between the propagation time difference and the characteristic position value.
In order to make it possible to use this method for diagnosis and for monitoring of, for example, a medium in a closed container, it is thus necessary to transmit electromagnetic pulses from an external area into the interior of the container, and vice versa. On the other hand, however, depending on the nature and characteristics of the medium stored in the container, it may be absolutely essential or at least of major importance to ensure that the container is sealed particularly well. Depending on the operating parameters in the container by virtue of the design, such as the pressure and temperature of the medium stored there, the electrical bushing which is used to pass electromagnetic pulses in and out is thus subject to particularly stringent requirements in some specific cases. This also applies to the transmission of an electromagnetic pulse from the containment surrounding the reactor pressure vessel to a pulse generator and to an evaluation and control unit, and vice versa.
In this case, by way of example, rigid coaxial conductors may be used to transmit electromagnetic pulses between the containment wall and the reactor pressure vessel, in particular in order to ensure the high signal quality which is required to ensure that reliable measured values are obtained. Nevertheless, however, it may be necessary to make the reactor pressure vessel accessible, for example for maintenance work. In order to allow this with only little effort even using rigid coaxial conductors, a coupling apparatus is desirable which allows segments of the coaxial conductor to be disconnected from one another and to be reconnected quickly and without any complications between the two bushings that have been mentioned.
In order to keep the interference with and the attenuation of the electromagnetic pulse as low as possible even at the coupling point in a system such as this, the coupling should satisfy stringent requirements. In particular, the impedances should be kept constant over the length of the conductor, or at least should not change with any discontinuities, so that disturbing reflections at sudden impedance changes are avoided as well as possible for the measurement. A high-quality electrical contact between conductors that are connected by means of the coupling is particularly important for reliable transmission of the electromagnetic pulse.